1. Field of the Invention
The present invention related to an image forming apparatus. More particularly, the invention relates to an improved developing unit and an image forming apparatus having the developing unit of the invention.
2. Description of the Related Art
An image forming apparatus is generally classified into a mono image forming apparatus and a color image forming apparatus. The mono image forming apparatus forms black and white image using a developer of only one color. The color image forming apparatus forms a color image using developers of different colors, for example, magenta, cyan, yellow and black.
An electro-photographic image forming apparatus forms an image on a printing paper according to the following step. A charging unit charges an image receiving medium, i.e., a photoconductor to have a predetermined level of an electric potential. A laser scanning unit radiates light on the photoconductor to form an electrostatic latent image. The electrostatic latent image is developed by a developer such as a toner, to form a toner image, and the toner image is transferred to a printing paper. A color image forming apparatus may include a plurality of developing units per each color and each of the developing units has its own photoconductor. Each of color toner images is formed on a corresponding photoconductor. The formed toner images of each color are transferred to an intermediate transfer medium such as a transfer belt in an overlapping manner. The overlapped color image is finally transferred to a printing paper. The color image is overlapped and transferred to a printing paper by processing through a set of predetermined operations and outputted.
Meanwhile, the plurality of developing units is an expendable supply. The developing units are attachable at a mounting frame disposed inside the image forming apparatus. The developing unit includes the photoconductor, a developer roller and a developer supply roller. The developing unit also includes drive gears at one side thereof to drive the rollers. The drive gears are in gear with driving gears positioned inside the image forming apparatus when the developing unit is attached at the mounting frame.
The developing unit is mounted at the mounting frame by a customer or a service provider. For convenience, the developing unit is mounted on the mounting frame while maintaining a predetermined gap between the developing unit and the mounting frame. A predetermined width of the gap is provided between the both ends of the developing unit and the mounting frame in a longitudinal direction of the photoconductor. The developing unit is supported by at least four points when the developing unit is completely mounted on the mounting frame in order to minimize the vibration generated from the image forming apparatus.
However, the gap may cause the coupling of the driving gears to loosen the drive gears. Therefore, less driving power is transferred to the drive gears than an ideal driving power. As a result, the photoconductor and the developer roller are driven with insufficient driving force. Furthermore, if the driving gears and the driven gears are not completely geared together, greater vibration occurs between the driving gears and the driven gears. As a result, the image quality degrades.